1. Field of the Invention
The present invention relates to a disc drive apparatus mounted with an improved clamping mechanism for clamping a recording medium in disciform, which drives a recording medium in disciform being clamped by the improved clamping mechanism to rotate.
2. Description of the Related Art
It has been required for a disc apparatus for recording information on or reproducing information from a recording medium in disciform such as an optical disc to be thinner in profile as market demand. In this connection, the same market demand is also directed to a disc drive apparatus mounted with a clamping mechanism for clamping a disc. The disc drive apparatus to be installed in such a disc apparatus is constructed by a motor that drives a disc being clamped by the clamping mechanism to rotate.
One example of such a disc drive apparatus, which has realized a thinner profile, was disclosed in the Japanese publication of unexamined patent applications No. 2005-253239.
As shown in FIG. 1 of the Japanese publication of unexamined patent applications No. 2005-253239, the disc drive apparatus is mounted with a spindle motor and a clamping section that includes a center cone, a plurality of clamping claws and springs, wherein the springs extrude the plurality of clamping craws in outward directions respectively. The spindle motor of the disc drive apparatus is provided with a cylindrical section that is a part of a rotor frame (hereinafter referred to as rotor yoke), which protrudes cylindrically. A shaft, which is supported by a sliding bearing of the spindle motor, is inserted into the cylindrical section and fixed therein, and then the clamping section is fixed on an external surface of the cylindrical section.
In the above-mentioned disc drive apparatus, a disc is clamped between the plurality of clamping craws of the clamping section and the rotor yoke.
On the contrary, in the case of the above-mentioned disc drive apparatus, total thickness in the axial direction of the disc drive apparatus is regulated by a total sum of respective length in the axial direction of the sliding bearing, length in the axial direction of the cylindrical section of the rotor yoke and clearance between the rotor and the stator.
With respect to the length in the axial direction of the cylindrical section out of the above-mentioned length regulating the total thickness of the disc drive apparatus, the cylindrical section into which the shaft is inserted, supports the rotor yoke and a disc loaded thereon, and further bears up force to be applied to the clamping section. Consequently, there existed minimal length with respect to the length in the axial direction of the cylindrical section at the least.
More specifically, in case the thickness of the rotor yoke is 0.5 mm, for instance, it is necessary for the length in the axial direction of the cylindrical section to be more than 2.0 mm at the least.
In case the thickness of the rotor yoke is less than 0.5 mm, there is a possibility of failing to maintain accuracy of cylindricality of the cylindrical section when relatively large force even within normal range of use is applied to the cylindrical section although a nitriding process is applied to the cylindrical section as disclosed in the Japanese publication of unexamined patent applications No. 2005-253239. In case the accuracy of cylindricality can not be maintained, it possibly occurs that the rotor yoke tilts with respect to the shaft or a position in the axial direction of the rotor yoke is shifted.
On the contrary, in case the thickness of the rotor yoke exceeds 0.5 mm, it is possible to make the length of the cylindrical section to be less than 2.0 mm. However, length in the axial direction of the clamping member, the bearing or a driving section of the motor must be shortened in proportion to increase of the thickness of the rotor yoke. Consequently, it is hardly realized for the disc drive apparatus to be made thinner in profile.
Further, possible length of the cylindrical section, which can be shortened, is extremely small in proportion to thickness of the rotor yoke.
Accordingly, it is hardly realized for the disc drive apparatus to be made remarkably thinner in profile.
On the other hand, it is desirable for the length in the axial direction of the sliding bearing to be longer as long as possible.
In other words, an extremely narrow gap is intentionally provided between the shaft and the sliding bearing so as to allow the shaft to rotate freely. As a result of the gap, the shaft possibly tilts with respect to an axis of rotation within some extent.
Accordingly, in order to reduce the tilt of the shaft, engaging length of the shaft with the sliding bearing is desirable to be longer as long as possible.
As mentioned above, in the disc drive apparatus disclosed in the Japanese publication of unexamined patent applications No. 2005-253239, a position in the axial direction of the top end portion of the sliding bearing is regulated by the rotor yoke.
Further, a disc is loaded on the top surface of the rotor yoke, so that it is necessary for a loading position of the disc to be moved upward in case the length of the sliding bearing is extended.
Accordingly, thickness of a disc apparatus for loading a disc as well as thickness of the disc drive apparatus is obliged to be thicker, and resulting in hardly coping with the market demand of making thinner in profile.
Furthermore, when driving a disc, a center of gravity of the rotating part, that is, a center of gravity of the rotor approximately positions at a center of the disc being clamped. However, the top end portion of the sliding bearing is located at a position below the disc. As a result, the center of gravity of the rotor is located at a position far from the sliding bearing that supports the rotor in the axial direction, and the rotor of which the center of gravity is located at a higher position results in being unstable with respect to the center of gravity.
More, unbalanced side pressure in relatively strong force is applied to the sliding bearing, so that load on the sliding bearing increases.
Accordingly, there existed a problem such that a life of the sliding bearing was shortened.